Stretching of filaments or threads



March 17, 1942. F. B. HILL ETI'AL STRETCHING 0F FILAMENT$ OR THREADS 2 Sheets-Sheet 1 Filed Jan. 22, 1941 March 17, 1942.

F. B. HILL ETAL STRETCHING OF FILAMENTS OR THREADS Filed Jan. 22, 1941 2 Sheets-Sheet 2 Patented Mar. 17, 1942 STRETCHIN G OF FILAMENTS OR THREADS Frank Brentnall Hill and Maitland Walton Alford, Spondon, near Derby, England, assignors to Celanese Corporation of America, a col poration of Delaware Application January 22, 1941, Serial No. 375,420 In Great "Britain January 23, 1940 12 Claims. (CI. 28-59) This invention relates to the stretching of materials in the form of filaments or threads, and is particularly concerned with stretching operations carried out in apparatus in which the material to be stretched is fed into a stretching chamber containing a fluid softening medium (e. g. moist steam or hot water) under pressure, from another chamber (a feed chamber) containing means for determining the delivery rate of the material into the stretching chamber, the feed chamber also containing a fluid (generally air) under pressure, but less than the pressure in the stretching chamber.

The presence of the fluid under pressure in the feed chamber minimizes the flow of the softening medium in the stretching chamber proper through the orifices by which the material is led into the stretching chamber, and thus prevents the adverse efiect on the material under treatment that would result from a high velocity flow of fluid under pressure from the stretching chamber in close proximity to the material passing through the orifices and in the opposite direction to the movement of the material. Apparatus of this character is described in U. S. Patents Nos. 2,142,909 and 2,142,910. a

The object of the present invention is to maintain the necessary pressure difference between the stretching chamber and the feed chamber, not only during the stretching operation proper but also during the starting-up operation. The invention is also concerned to make the whole starting-up operation substantially automatic in character, and generally to reduc the difficulties attendant on bringing up the materials to the full degree of stretch.

According to the invention, a method of stretching materials-in the form of filaments or the admission of fluid to the other chamber so as to render the pressure in said other chamber dependent on th pressure in the first chamber and to maintain the desired difference in pressure both during the raising of the pressures to their working levels and during their maintename at those levels.

' of the diaphragm and the valve.

In this way, it is merely necessary to admit pressure medium toone chamber and the pressure of the medium in the other chamber automatically follows with the a lower pressure, is eliminated.

In order to control the pressure in one chamber by means of the pressure in the other, the medium supplied to the controlled chamber may be supplied through a valve actuated by a diaphragm communicating on one side with the pressure in the controlling chamber and on the other with the pressure in the controlled chamber. A spring of predetermined strength co-operates with the diaphragm to determine the position of the valve, so that the difference in pressure on the two sides of the diaphragm is either balanced by the spring, or distorts the diaphragm and actuates the valve so as to change the pressure in the controlled chamber until the required pressure difference is obtained. Since, however, the pressure difl'erence desired between the two chambers is fixed by other considerations, it may not be of a. suitable magnitude to eflect the. control of the valve with the sensitivity required. Accordingly,

it is preferable to employ, on one or both sides of' the diaphragm, a controlled pressure from an independent supply of pressure fluid, maintained at a constant difference from the pressure in one of the chambers, preferably the controlled chamber, the constant amount of diiference being conveniently adjustable so that the order of magnitude of the pressure difierence on the two sides of the diaphragm is appropriate to the characteristics The controlled pressure required for this purpose may be provided for by allowing the independent supply to escape through a leak controlled by a valve actuated' bya further diaphragm, exposed onone side to the pressure in the chamber and on the other to the pressure between the valve and the leak, which latter pressure is also the controlled pressure required. The further diaphragm is loaded by a spring, which may conveniently be made adjustable. The leak may either be a fixed leak, or may be variable, being controlled by a further valve, mechanically coupled to work in the opposite sense to the first, and disposed in series therewith in the independent supply.

In addition to providing a certain means for ensuring that the required pressur difference exists during the starting-up operation proper, the invention has the big advantage of enabling the starting-up to be carried out very rapidly, and at the same time minimizes the danger of threadbreakage during starting-up and reducing the amount of waste produced in the interval before full stretch is reached.

The invention may be generally applied, by the selection of a suitable softening agent, to materials in the form of filaments or threads. It is particularly advantageous as applied to threads or bundles of continuous filaments of organic derivatives of, cellulose, such as the cellulose esters, e. g. cellulose acetate, formate, propionate and butyrate, mixed esters, e. g. cellulose acetatepropionate and aceto butyrate, and cellulose ethers, e. g. methyl, ethyl and benzyl cellulose.

By way of example one arrangement of apparatus suitable for carrying out the invention, and incorporating the means for starting the stretching operation described in U. S. application Ser. No. 372,108 filed December 28, 1940, will now be described in greater detail with reference to the accompanying drawings in which:-

Fig. 1 is a diagrammatic view of the apparatus as-a whole, and

Figs. 2-4 are more detailed views of the steam supply valve, the air supply valve and the setting valve respectively, shown diagrammatically in Fi 1.

In the apparatus shown in Fig. 1' a number of threads I are taken from bobbins 2 mounted in a creel 3, are led through guide-eyes 4 in connection with the creel 3 and proceed from the guide-eyes 4 to a spacing comb 5. From the comb 5 the threads I enter a stretching apparatus of the general form described in U. S. Patent No. 2,142,909.

This comprises a feed chamber 5 having apertures I through which the threads enter and containing nip-rollers 8 by. means of which the rate at which the threads are drawninto the stretching apparatus is accurately controlled. From the feed chamber 6 the threads I pass to a stretching chamber 9, entering through apertures I and leaving through apertures During the stretching operation the stretching chamber 9 is supplied through a pipe I2 with moist steam under pressure and the feed chamber Ii is supplied with compressed air through a pipe I3. The compressed air in the chamber 6 is supplied at a pressure slightly lower than that of the steam in the chamber 9 and minimises the fiow of steam from the chamber 9 through the apertures I 0, so that the threads, softened in the chamber 9, are not broken by being blown back into the chamber 5.

During the initiation of the stretching operation the supply of both steam and air through the pipes I2 and I3 respectively is at first shut oil, so that the threads I may be led through the chambers 6 and 9. The threads emerging from the apertures II are gathered as a rope, which passes round a fixed guide pulley I4, round which it turns at an angle of approximately 90, and proceeds to a guide pulley mounted on a vertical axis on a comp nsat r bar I6 pivoted at '|I and carrying a further pulley IS on a horizontal axis at its other end. A spiral spring l9 urges the compensator bar I6 in a counter-clockwise direction from above, and the pull of the threads I between the pulleys I4 and I5 initially counteracts the pressure of the spring I9. The compensator bar I6, with its pulleys I5 and I8 and spring |9 together constitute the tension-sensitive means described and claimed in U. S. application Ser. No. 372,108 filed December 28, 1940. The pulley I8 guides the rope of threads I to a conical roller made up of three parts 2|, 22 and 23, the parts 2| and 23 being cylindrical and having diameters proportional respectively to the unstretched length of the threads and the' stretched length desired. The part 22 is the conical part, and connects the parts 2| and 23. The length of the part 22 and the position of the point II are arranged,so that the pulley I8 is always close to one or other of the parts 2|, 22, 23 and guides the threads I passing over it accurately to the conical roller, to the under side of which the threads pass.

Co-operating with the large part 23 'of the conical roller is a further roller 24 constituting, with the roller 23, a pair of nip-rollers similar to the rollers 8 in the chamber 6, beyond the rollers 23 and 24 there are a further comb 25,

a set of three drying drums 26, a further comb 21, a pair of mangle rollers 28 and the take-up creel for the collection of the stretched threads. The comb 21 and the mangle rollers28 are wider than the nip rollers 8 and 24, being of a size appropriate to the width of the take-up creel, the creel comprising ,a waste swift 29 and take-up bobbins 3|.

The steam is fed by the pipe I2 to the stretching chamber 9 through a steam valve 32 under the control of pressure-sensitive pressure controller, indicated generally at 33, operated by compressed air, The steam valve 32 is adjusted, to maintain'a desired steam pressure in the steam chamber 9, by means of a spring-loaded diaphragm 34 subjected on one side to an air pressure supplied through the controller 33.

Air is supplied to the controller 33 at a pressure of 1'? pounds per square inch from the air supply main I3 and valves 35, 35 through a branch pipe 31 and a suitable reducing valve 38. The air so supplied is able to pass through one valve 39 into a pipe 40 communicating with the diaphragm 34 of the steam valve, and is able to pass from the pipe 40 through another valve 4| controlling a leak 42, whereby the air may escape into the atmosphere. The two valves 39, 4| controlling the air in this manner are coupled together by a member 43, so that as one opens the other is closed, and by these means the air pressure applied to the diaphragm 34 of the steam-controlling valve 32 is varied. Thus, by opening the valve 39 by which the air reaches the diaphragm 34 and by closing the valve 4| by which the air escapes through the leak 42, the pressure applied to the diaphragm 34 may be increased to any degree up to a limit of 17 pounds per square inch, while by closing the valve 39 and opening the valve 4|, the pressure applied to the diaphragm 34 may be reduced, if necessary to atmospheric pressure. The position of the coupled valves 39, 4| controlling the air is determined by the air pressure in a bellows 44, the bellows being in communication with an air line through which air from the supply at 1'7 pounds per square inch, after passing through a controlled leak to'the atmosphere.

a suitable fixed throttling device 59, escapes by The controlledleak is in the form of a nozzle from which the exit of the air is opposed by a pivoted flapper 52. The flapper 52 is connected by a lever and'link 46, 41 to a pressure sensitive element 53, in the i'orm of a Bourdon tube subjected through a pipe 54 to the pressure in the steam chamber 9, i. e. the pressure it is desired to control. When the pressure in the steam chamber 9 is high, the flapper 52 is pivoted closer to the nozzle 5|, so increasing the pressure in the air line 45-behind the nozzle, and when the steam pressure is low the flapper 52 is pivoted away from the nozzle 5| and reduces the pressure behind the nozzle. Accordingly, the pressure in the bellows 44 in communication with the air line 45 is made to depend upon the pressure in the steam chamber 9, a high pressure in the steam chamber 9 increasing the pressure in the bellows 44, while a low pressure decreases the pressure in the bellows. The expansion of the bellows 44, and the consequent movement to the left of the member 43 are arranged to close the valve 39 admitting air to the steam-valve diaphragm 34 and to open the valve 4| by which air escapes through the leak 42, and the resulting drop in the pressure applied to the diaphragm 34 closes the steam valve 32 and reduces the steam pressure. By these means, the pressure in the steam chamber 9 is maintained at the desired level. A pen 55 is secured to the flapper 52, so as to record on a chart 56 the pressure in the steam chamber 9 as communicated to the pressure sensitive element 53 controlling the flapper 52.

In order to adjust the desired pressure in the steam chamber 9, the nozzle 5| which co-operates with the flapper 52 is itself capable of being pivoted, about the same axis 51 as the flapper 52, and is adjustable through links 58 and levers 59 from a setting control 60 outside the pressuresensitive pressure controller 33. The pressure that the controller 33 is thus set to give is indicated by a pointer 6|, disposed in a suitable position to be compared with the pen 55 connected to the flapper 52, and under the control of the same connections 58, 59 as the nozzle 5|.

In order to reduce the sensitivity of the con- I troller 33, so as to avoid hunting, the air escaping from the nozzle 5| is caused to pass through an elastic bellows 62 adapted to absorb any violent fluctuations of pressure behind the nozzle. For the same purpose. a leak 63 is pro-, vided in the air line 45 immediately before the elastic bellows 62. The leak 63 is controlled by a valve 64, which may be adjusted so as to adjust the sensitivity of the controller 33 and is coupled with a throttling valve 65 in the air line 45. The two valves 62, 64 are adjusted together by hand. When the leak 63 is shut and the throttling valve 64 full open, the sensitivity is greatest: By slightly opening the leak 63 without much afiecting the throttling valve 64 the sensitivity may be reduced. By widely opening the leak 63 and nearly closing the throttling valve 64, the leak at the nozzle 5| is rendered ineffective, and the steam valve 32 may then be controlled by hand, by manipulating the reducing valve 38 through which air is supplied to the controller 33.

As an additional precaution against hunting, means are provided whereby relative movements between the nozzle 5| and the flapper 52 are damped, any movement of the flapper 52 being at first accompanied by a corresponding movement of the nozzle 5|, the nozzle returning after a time to its original position. For this purpose the nozzle 5|, in addition to being under the control of the hand setting device 69, may have, superposed on that control a further control depending on changes of pressure behind the diaphragm 34 controlling the steam valve 32. The nozzle 5| is connected by means of a link 68 to one arm 61 of a bell-crank lever, which is pivoted-at 68 on another lever 69, actuated by the setting control 69 of the controller 33 and actuating the pointer 6| showing the pressure to which the controller is set. The 'other arm 19 of the bell-crank lever is connected by a frame TI and link I2 to a point I3 between two elastic bellows 14, 15, both of which communicate with the space behind the diaphragm 34 of the steam valve 32. One of these bellows |4, communicates directly with this space and the other, 15, through a substantial capillary resistance 16. Thus, any change in pressure behind the diaphragm 34 is immediately communicated to the bellows 14, so that the point of connection 13 between the bellows 14, I5 is moved and consequently through the bell-crank lever 61, 19 and the link 66, the nozzle 5| is moved. After a time lag, depending on the magnitude of the capillary resistance 16, the same pressure is communicated to'the other bellows 15 which acts against the bellows l4 and restores the nozzle 5| to its original position.

The compressed air for the feed chamber 6 is supplied through an air-supply valve I1 actuated by a spring loaded diaphragm 18, one side of Which is exposed to the pressure of the steam in the stretching chamber through a pipe I9 branching oil? the pipe 54. The other side of the diaphragm 18 is subjected to an air pressure existingbetween a pair of coupled valves 89, 8| through which, in series, air supplied from the air main 35 escapes by a leak 82. The coupled valves 88, 8| together constituting a setting valve, are actuated by a diaphragm 83, loaded by a spring 8,4 whose pressure is adjustable by means of a screw 85, and exposed on one side, through a pipe 86,'to the air pressure in the feed chamber 6, and on the other to the pressure between the coupled valves 89, 8|. By adjusting the spring 84 co-operating with the setting valve diaphragm 83, the difference in pressure maintained on the two sides of the diaphragm 83 may be adjusted to any constant amount, for, unless the pressure difierence balances the force of the spring 84, the diaphragm 83 will be distorted, and the setting valve position altered until balance is obtained. In this way the air supplied to the feed chamber l6 through the air-supply valve I1 is under the control of a diaphragm 18, which is exposed on one side to the steam pressure and on the other to a pressure differing by a constant amount from the pressure in. the feed chamber 6. Thus, any change in the steam pressure is communicated to the valve 11 controlling the air supplied to the feed chamber 6 and produces a corresponding change of air pressure in the feed chamber 6.

The valves 32, 11 and and 8| ar shown in greater detail in Figs. 2-4. In Fig. 2, the valve 32 is shown as a double conical member 99 closing on seats 9|, 92, and actuated by a spindle 93 secured to the diaphragm 34. A spring 94, enclosed in a chamber 95 acts through the spindle 93 to load the diaphragm 34. The diaphragm forms one side of a chamber 96 the pressure in which, through the pipe 91, is controlled by the controller 33 of Fig. 1. Members 98 locate the chamber 95 and valve 32 relatively to one another. The valve 11 as shown in Fig. 3is very similar to the valve 32 shown in Fig. 2, except that, instead of the members 98 a chamber 99 encloses the lower side of the diaphragm, indicated at I8. The chamber 99 communicates, by the pipe I00, with the line between the valves 80, 8|.

The setting valve shown in Fig. 4, incorporates the valves 80, 8|, the former comprising a plate IOI facing a nozzle I02, and the latter a needle I03 controlling the leak 82 The plate IOI and needl I03 are mounted on a sliding piston I04, grooved at I05 for the passage of air to the leak 82, and secured .by a member I06 to the diaphragm 83. The spring 84 loading the diaphragm 83 is enclose-d in a chamber I01 communicating by the pipe 86 to the feed chamber. Thus the diaphragm 83 is exposed on one side to the pressure in the chamber 6, and on the other to the pressur on the low pressure side I of the valve 80. The valves 35, 36 in the main air supply I3 are, respectively, a reducing valve, for bringing the air supply down to a convenient pressure of about 60 lbs..per square inch, and a stop valve for the purpose of closing down. A reducing valve Y81, and a stop valve 08 are provided in the main steam supply I2 for similar purposes. The reducing valves 35, 35 and 81 are adjusted, and the stop valve 31 opened before the apparatus is started up, the air still being under the control of the air supply valve I1, which is shut.

In starting up the device the threads I are drawn from the bobbins 2 and threaded through the comb 5 and through the chambers 6 and 9, being collected in the form of-a rope at the pulley I4 and proceeding as a rope round the pulleys I5 and I8 and on to the small end 2I of the conical roller. The nip-rollers 8 and the conical roller are then driven at such a speed that the peripheral speed of the nip-rollers 8 is equal to that of the small part 2I of theconical roller.

The steam stop ,valve 81 is then opened and the pressure-sensitive pressure controller 33 allows the steam valve 32 to admit ,steam to the steam chamber 9, and at the same time the interconnection 54, I9 between the steam chamber 9 and the air valve 11 for the feed chamber 6 admits air to the latter at a lower pressure, determined by the strength of the spring in the air su pply valve 11, and the adjustable spring 80. The steam pressure rapidly builds up, the air pressure following with the predetermined differenc until full pressure is reached in both chambers, at which time the controller 33 operates to keep the two pressures steady and at the required difference. During this short interval of time, the conical roller 2 I, 22, 23 draws the increasingly softened threads, in the manner described in U. S. application Ser. No. 372,108 filed December 28,1940, at a faster and fastenrate until the full stretching rate is reached. Then, as in that specification, the threads I are unhooked from the pulleys I4, I5 and I8, cut \on the roller 23 and led over the comb 25-round the drying drums 26, over the comb 21, through in the stretching chamber 9, the possibility of breakdown in the period during which the stretch is brought up to full amount is much reduced. Moreover, this period can be considerably shortened, with consequent diminution in the amount of waste, and higher thread-speeds may be employed, especially in view of the ability of the conical roller 2|, 22, 23 to pull the threads I precisely in accordance with their ability to receive stretch. The apparatus needs less attention, since after the threads I have initially been passed through the apparatus from the supply creel 3 to the conical roller 2I, 22, 23 it is only necessary to start the drive to the feed-rollers 8 and conical roller 2I, 22, 23, and open the air and steam stop valves 36 and 08 for the stretch to be applied at an increasing rate until the full degree of stretch is reached.

The apparatus, including the improved takeup device of U. S. application Ser. No. 372,108 filed December 28, 1940 also makes it possible to shut down the operation with little danger of thread breakage, since turning off the steam stop valve 88 does not prevent the necessary pressure difference being maintained as both steam and air pressures fall, and the conical roller 2|, 22, 23 compensates for the diminished ability of the material to stretch until a condition of no-stretch is reached, when the drive to the feed-rollers 0 and the conical roller 2|, 22, 23 can be'stopped.

The apparatus is capable of handling threads or thread bundles over a wide range of size, so that it lends itself to the economical stretching of filaments for a variety of purposes. Thus, apart from producing fine threads (e. g. 30 denier) of stretched filaments for use as such or for doubling .higher than the pressure of the fluid in said feed chamber, said method comprising admitting the respective pressure fluids to the feed and stretching chambers to raise the pressures in said chambers to their working levels after the material has started to run through the stretching chamber, and employing the pressure of the fluid in one of said chambers to control the admission of fluid to the other chamber so as to render the pressure in said other chamber dependent on the pressure in the first chamber and to maintain the desired difference in pressure both during the raising of the pressures to their working levels and during their maintenance at those levels.- i

2. Method according to claim 1, comprising maintaining a pressure at a constant difference from that in one of said chambers and employing said pressure to control the admission of fluid to the other of said chambers.

3. Method of stretching materials in the form of filaments or threads in which the material is drawn under tension from a feed chamber into and through a stretching chamber containing a fluid softening medium under a pressure slightly higher than the pressure of the fluid in said feed chamber, saidmethod comprising employing the pressure of the fluid-in one of said chambers to control the admission of fluid to the other. chamber so as to render the pressure in said other chamber dependent on the pressure of the first chamber and to maintain the desired difference of pressure between the chambers, and shutting off the supply of pressure fluid to the controlling chamber to permit the pressure in both chambers to fall, thereby enabling the pressure differ-- ence to be maintained while bringing the stretching operation to an end.

4. Method of stretching materials in the form of filaments or threads in which the material is drawn under tension from a feed chamber into and through a stretching chamber containing a fluid softening medium under a pressure slightly higher than the pressure of the fluid in said feed chamber, said method comprising admitting the respective pressure fluids to the feed and stretching chambers to raise the pressures in said chambers to their working levels after the material has started to run through the stretching chamber, and employing the pressure of the fluid in the stretching chamber to control the admission of fluid to the feed chamber so as to render the pressure in the feed chamber depending on the pressure in the stretching chamber and to maintain the desired difference in pressure both during the raising of the pressures to their working levels and during their maintenance at those levels.

5. Method of starting up an operation for stretching material in the form of filaments or threads by applying tension to said material while it is drawn under tension from a feed chamber.

into and through a stretching chamber containing a fluid softening medium under a pressure slightly higher than the pressure of the fluid in said feed chamber, said method comprising admitting the respective pressure fluids to the feed and stretching chambers to raise the pressure in said chambers to their working levels after the material has started to run through the stretching chamber and employing the pressure of the fluid in one of said chambers to control the admission of fluid to the other chamber so as to render the pressure in said other chamber dependent on the pressure in the first chamber and to maintain the desired difference in pressure both during the raising of the pressures to their working levels and during their maintenance at those levels and changing the degree of stretch effected by placing the output-input speed ratio of the material under the control of the tension in the material as it leaves the softening medium to control the stretching rate and to increase said rate up to a desired limit as said tension falls in consequence of the increasing softening influence of said medium as the pressure of said medium is raised to its working level.

6. Method of terminating an operation for stretching material in the form of filaments or threads in which the material is drawn under tension from a feed chamber into and through a stretching chamber containing a fluid softening medium under a pressure slightly higher than the pressure of the fluid in said feed chamber, said method comprising employing the pressure of thefluid in one of said chambers to control the admission of fluid to the other chamber so as to render the pressure in said other chamber dependent on the pressure in the first chamber and to maintain the desired difference in pressure between the chambers, shutting on the supply of fluid to the controlling chamber to permit the pressure in both chambers to fall while still retaining the pressure difference and placing the speed at which the material leaves the softening medium under the control of the tension in the material as it leaves the softening medium whereby said speed and the consequent rate of stretching are diminished as said tension falls in consequence of the decreasing softening influence of said medium resulting from the supply being shut off.

7. Apparatus for stretching materials in the form of filaments or threads, said apparatus comprising a feed chamber, a stretching chamber, means for supplying a fluid softening medium under pressure to said stretching chamber, means for supplying a fluid under pressure to said feed chamber, control means in association with one of said supply means for raising the pressure in the chamber supplied thereby, for maintaining the pressure at a desired level, and for cutting down the supply of pressure fluid, and control means in the other of said supply means, under the influence of the pressure in the chamber supplied by the first of said supply means, for controlling the admission of fluid to the other chamber, so as to render the pressure in said other chamber dependent upon the pressure inthe first, and to maintain a desired pressure difference between said chambers during the raising, maintenance, and cutting down of the pressures in both chambers.

8. Apparatus for stretching materials in the form of filaments or threads, said apparatus comprising a feed chamber, a stretching chamber,

' means for supplying a fluid softening medium under pressure to said stretchingv chamber, means for supplying a fluid under pressure to said feed chamber, first and second valves in the respective supplies to the chambers to control the admission of respective fluids to the chambers, a diaphragm enclosed on both sides and actuating the second valve, a communication from one side of said diaphragm to a pressure depending on that in one of said chambers and a communication from the other side of the said diaphragm to a pressure depending on that in the other of said chambers, the diaphragm and the valve actuated thereby serving to render the pressure in said other chamber dependent upon the pressure in the first, and to maintain a desired pressure difierence between said chambers during the raising, maintenance, and cutting down of the pressures in both chambers.

9. Apparatus for stretching materials in the form of filaments or threads, said apparatus comprising a feed chamber, a stretching chamber, means for supplying a fluid softening medium under pressure to said stretching chamber, means for, supplying a fluid under pressure to said feed chamber, first and second valves in the resp'ective supplies to the chambers to control th admission of respective fluids to the chambers, a diaphragm enclosed on both sides and actuating the second valve, a third valve connected to the same fluid supply as the second valve, a constricted l-eak beyond said valve, a second diaphragm enclosed on both sides and actuating said third valve, one side of the second diaphragm amount'therefrom, a communication "from the leak side of the third valve to one side of the first diaphragm and a communication from the other side of the first diaphragm to the other of said chambers, the first diaphragm and the second valve actuated thereby serving to maintain a desired pressure difference between said chambers during the raising, maintenance, and cutting down of the pressures in both chambers.

10. Apparatus according to claim 9, wherein the third valve is mechanically coupled to a fourth valve in series therewith, the fourth valve being adapted to vary the constriction of the leak and the two valves working in opposite senses, a communication from the leak side of the third valve to one side of the first diaphragm being provided between the two coupled valves.

11. Apparatus according to claim 9, wherein means are provided for adjusting the spring b which the second diaphragm is loaded.

12. Apparatus for stretching materials in the form of filaments or threads, said apparatus comprising a feed chamber, a stretching chamber, means for supplying a fluid softening medium under pressure to said stretching chamber, means for supplying a fluid under pressure to said feed chamber, means in the feed chamber for positively feeding material into the stretching chamber, a conical roller for positively drawing the material out of the stretching chamber, control means in association with one of said supply means for raising pressure in the chamber supplied thereby, for maintaining the pressure at a desired level, and for cutting down the supply of pressure fluid, control means in the other of said supply means under the influence of the pressure in the chamber supplied by the first of said supply means for controlling the admission of fluid to the other chamber so as to render the pressure in said other chamber dependent upon the pressure in the first and to maintain a desired pressure difierence between said chambers during the raising, maintenance, and cutting down of the pressures in both chambers, tensionsensitive means adapted to engage the material as it leaves the stretching chamber and guide means under th control of said tension-sensitive means for varying the point along the axis of said roller to which the material is guided so as to vary the amount of stretch imparted between the conical roller and the feeding means inversely with the tension in the material as it leaves said chamber.

FRANK BRENTNALL HILL. MAI'I'LAND WALTON ALFORD. 

